A strain-rate-dependent analytical model for composite bolted joints

In the present research, a novel analytical approach was developed to predict the bearing chord stiffness and the damage initiation bearing-load of single-lap composite bolted joints under medium strain rate loading. First, the elastic moduli, Poisson's ratio, and strength of a unidirectional composite ply at an arbitrary strain rate were predicted by available micromechanical equations. Then, the bearing chord stiffness of the joint at any arbitrary strain rate was predicted. For this purpose, the available spring-based model was modified. The strain-rate-dependent damage initiation bearing-load of the joint was predicted by using the moduli and the stress concentration factor of a pin-loaded unidirectional ply. Four types of single-lap joints with [-45/0/+45/90]s and [90/-452/+45]s layups with and without carbon nanofibers were tested at the strain rates of 0.0048 s-1, 0.36 s-1, and 0.89 s-1. The results of experiments showed that mechanical properties of single-lap composite bolted joints increased with increasing the strain rate. Also, employing carbon nanofibers has a significant effect on the mechanical properties of the joints. The predicted results in comparison with the conducted experimental data show good agreements.